The present invention relates to force multipliers and more particularly to mechanical force multipliers.
The following description of the mechanical force multiplier of the present invention is directed to its employment in a diaphragm valve operator but may be employed in connection with other apparatus in other environments where mechanical force multiplication is required.
In a conventional diaphragm valve and air motor combination, a spring is required to exert its maximum force in the valve closed position. However, since the spring can only be compressed from the closed position, any movement of the spring from that point can only result in additional unnecessary force from the spring.
For example, a 3 inch weir diaphragm valve with 300 psi (pounds per square inch) line pressure requires 5,300 pounds of spring force to close the valve. Additional force exerted by compressing the spring when the valve is opened will result in 6,400 pounds of spring force, yet at full open, only 1,600 pounds of force is required.
A conventional air motor utilizes a direct communication between the diaphragm of the diaphragm valve and the spring and air motor assemblies. This direct connection delivers the same force to the valve diaphragm that is applied by the spring and/or the air motor.
For example, a direct acting air motor is a fail open operator. That is, if air pressure to the operator is ever broken, then the valve will be opened. A spring is used to maintain the open position or open the valve when air is removed from the air motor. The air motor is used to close the valve. The spring force and the force delivered from the air motor in excess of the spring force will act directly on the valve diaphragm through the valve spindle.
A second example is a reverse acting air motor. This is a fail close operator. If air pressure to the air motor is ever broken, the valve will be closed. A spring is used to maintain the closed position or to close the valve when air is removed from the air motor. The air motor is used to open the valve. The spring force and any air motor force in excess of the spring force is transmitted directly to the valve diaphragm through the valve spindle.
Other valve operators have used linkage arrangements or scissors mechanisms to actuate valves. These devices use a primary link system with either a handwheel or a small air motor reacting directly on the primary link system. These devices are either limited in stroke because angular movement is small, thus limiting the stroke; or unable to accomplish full force multiplication to benefit the air motor size. Also, these devices are not used as fail safe actuators.